An air gun is a rifle, pistol, etc., which utilizes a compressed gas to fire a projectile. Air guns may be powered by, for example, a coil spring loaded piston or an air-spring loaded piston.
Air guns powered by the coil spring loaded piston include a common trigger assembly, a coil spring assembly housed within a compression chamber of the rifle, and a barrel. The coil spring assembly includes a coil spring coupled to a piston. Cocking the gun moves the piston, which compresses the coil spring until a latch on the rear of the piston engages a sear on the trigger assembly. The coil spring assembly permits use of a center, i.e., an in-line latch, wherein the latch on the rear of the piston is generally in-line and concentric with a longitudinal axis of the piston. Actuating the trigger assembly releases the sear of the trigger assembly and allows the coil spring to decompress, pushing the piston forward, and thereby compressing the gas, i.e., air, in the compression chamber directly behind the projectile. Once the air pressure rises to a level sufficient to overcome any static friction and/or barrel restriction between the projectile and the barrel, the projectile moves forward within the barrel, propelled by an expanding column of gas.
The air-spring loaded piston includes a sealed compression cylinder disposed within the piston. The compression cylinder contains a gas, such as air or nitrogen. Cocking the gun moves the piston, which compresses the gas within the compression cylinder until the latch on the rear of the piston engages a sear on the trigger assembly. If the compression cylinder includes a single dynamic compression seal, i.e., if the compression cylinder includes only a single moving seal to contain the pressurized gas within the compression cylinder, then the trigger assembly must engage the piston at an outer surface thereof. In order to use the center, i.e., in-line latch generally associated with the coil spring loaded piston assembly described above, then a double dynamic seal compression cylinder may be utilized, i.e., the compression cylinder includes a center rod for engaging the center latch, and two moving seals to seal the compression cylinder against both the piston and the center rod.